1. Technical Field
The present invention relates to horizontal drilling into strata surrounding a well casing.
2. Description of the Related Art
Typically, oil and gas wells are vertically oriented structures going into the earth's strata to access oil and gas formations buried deep in the earth. In many cases, this vertical structure adequately taps into the petroleum formations. However, in most cases the petroleum is not stored in simple pools or caves that can be easily tapped. The petroleum is often in multiple pockets scattered at many levels and locations in an oil field. Often, various pockets of petroleum are positioned near existing wells but, because of the formation, the petroleum will not flow to the opening provided by the existing well. Digging a new vertical well to access these deposits is too expensive.
Various techniques have been developed to try to tap into nearby deposits to existing wells. Most of these techniques involve mechanical tools that must operate at some angle deep within a well. The goal is to provide a puncturing of the well casing and extension of the bore hole to a formation laterally positioned from an existing well. One technique for accomplishing this is provided by Bull et al., U.S. Pat. No. 3,958,649. Mechanisms such as that shown in Bull et al. use complex mechanical devices in harsh environments operating deep beneath the ground. Therefore, effective tools using these techniques are expensive to manufacture and difficult to use in the field.
There are a number of known methods for horizontally drilling into a formation surrounding an existing well. U.S. Pat. No. 4,640,362 to Schellstede teaches a method of penetrating a well casing and surrounding earth strata with the use of a punch member for cutting through the well casing. The punch member includes a retractable jet nozzle means for penetrating the surrounding earth's strata after the punch member has cut through the casing. An alternative technique is described in U.S. Pat. No. 5,413,184 to Landers. The latter patent describes a multi-step method that begins with the insertion of a flexible shaft having a ball cutter on an end thereof into upset tubing within a well casing. The upset tubing is provided with an elbow at its lower extremity for receiving the ball cutter therein. The ball cutter cuts a hole in the well casing and is then moved horizontally a given distance. The flexible shaft and ball cutter are then removed and a flexible tube having a nozzle blaster on the end thereof is then inserted into the upset tubing. A fluid of surfactant and water at high pressure is then pumped into the tube to cut an extension into the previously cut channel.